Metallurgy of zinc



y 10, 1960 E. WAINER METALLURGY OF zmc Filed Dec. 5, 1957 A T TORNE Y stead of the solid phase.

METALLURGY F ZINC Eugene Wainer, Cleveland Heights, Ohio,

Horizons Incorporated, Cleveland, of New Jersey Application December 5, 1957, Serial No. 700,906 3 Claims. (Cl. 7588) assignor to Ohio, a corporation This invention relates to the pyrometallurgy of zinc. More particularly it relates to the recovery of pure zinc metal from its vapor form. Since zinc is one of the more volatile elements, zinc is commonly recovered from impure metallic residues or from reducible zinc compounds by converting the zinc metal to a vapor, or by reducing the compound to metallic zinc and converting the zinc so formed into zinc vapor; Ineither event the undesired impurities or compound forming elements are separated from the zinc by the vaporization of the zinc leaving behind in either liquidor solid form the impurities asso' ciated with the source material.

The process ofobtaining pure zinc metal by condensation of zinc vapor is fraught with many dangers and difficulties as is well known in this art. The presence of even only trace amounts of oxygen or other oxidizing gases in the vapor phase or in the region where condensation is to be accomplished results in the production of blue powder, an undesirable contaminant which renders the zinc useless for most purposes for which the zinc is intended. -The blue powder is formed by the superficial oxidization of the zinc. Other contaminants also react with the zinc vapor and hence it is necessary to carefully selectthe materials of construction employed in zinc condense rs. In addition the recovery of the zinc in solid form, e.g. as a powder, is a tedious and wasteful operation because in many instances the powder must be remelted for ultimate use. Furthermore the handling incident to the use of powder, wastes time and labor and requires facilities for packaging and unloading which are not used when the metal vapor is condensed to the liquid phase in- However, the conditions under which zinc can be recovered as a pure liquid metal by condensation from zinc vapor are even more exacting than the procedures whereby a pure zinc powder is obtained from zinc vapor.

In accordance with the present invention it has been found that substantially pure zinc may be recovered in the form of liquid zinc by producing zinc vapor from any suitable source material and bringing the zinc in the vapoi' phase into contact with a condensing surface located within the furnace chamber wherein the vapor is produced. In addition it has been found that to obtain pure zinc liquid, the condensing surface must be maintained at a critical temperature, and the liquid droplets formed thereon must be collected as they form, by means of a suitable apparatus whereby oxidation or other chemical reaction of the metal collected is virtually eliminated to the point of being non-existent. The critical temperatures of the surface on which the vapor is condensed have been found to lie between 530 C. and 550 C., and it has been found that all other surfaces in the region of the condensing surface must be maintained at slightly higher temperatures in order to insure that the condensing surface provided is the only surface on which condensation is permitted to occur in a controllable manner. The condensing surface may be formed of graphite or other inert forms of carbon, or SiC or even a ceramic material. As

will be seen from the drawings which follow, the condensing surface is located in the free space into which the zinc is vaporized from a pool of molten material below the free space or it may form a boundary of that space, for instance when it forms a wall portion of the furnace or reaction vessel.

In order to minimize the opportunity for the formation of undesirable by-products, I have found that the zinc should be condensed as soon as possible after it is evolved from the reaction zone. I have found that the means for effecting condensation of the zinc should, in consequence,

be located within the vaporizing or reducing furnace itself rather than in a side arm or olftake as has commonly been the practice in the prior art.

The method and apparatus forming the present invention will be more fully understood from the accompanying drawing in which:

Figure 1 is a fragmentary view in section of one embodirnent.

Figures 2 and 3 are similar fragmentary sectional views of additional embodiments.

For purposes ofillustration the figures will be described with reference to the treatment of metallic zinc residues, although it will be evident to others skilled in the art that by suitable modifications, the apparatus will be equally adapted to the treatment of zinc compounds for the recovery of pure zinc by their decomposition.

In the figures there is shown schematically a furnace pot 10 and one or more heaters 12 adapted to melt a charge of impure metallic zinc in the pot 10. Above the melt as shown in Figure 1 there is a free space 20 into which Zinc vapor passes directly from the pool of molten zinc, whenever the conditions of temperature and pressure in the furnace are such that zinc can exist in the form of a vapor. The furnace it is arranged so that a finger-like member 16 extends well into a free space 20 above the melt. Preferably the distance between the portion of finger 16 closest to melt 14 is no greater than that required to avoid any splashing of material from the melt 14 onto the surface 16. The finger is provided with means 17 for controlling its temperature so that it may be maintained at any temperature at or above the melting point of zinc and specifically at temperatures between 530 C. and 550 C. The condensing finger, for example, may be hollow and may be provided with an electrical resistor positioned in a centrally located cavity, in the manner shown in U.S. Patent 2,781,189. Alternatively, a heating or cooling fluid may be passed through a hollow heat exchanger positioned in the finger and forming a portion of a suitable thermostatically controlled circuit. Other means for maintaining the temperature of the outer surface of finger 16 within the range of 530' C. and 550 C. will be readily apparent and I do not wish to be restricted to any specific means described merely by way of illustration. Beneath the finger 16 shown in Figure 1 there is a trough 22 which slopes downwardly and out wardly from the center of the furnace it) and extends to a catch basin 23 in which the zinc is collected. By suitable liquid seals (not shown), the evolution of other contents of the furnace may be prevented. After it is collected, the molten metal may be converted to pigs by casting as is conventional in this art. Suitable means (not shown) may be provided for draining any sludgeor other accumulation of impurities from the furnace either intermittently or continuously.

The condensing surface may be supported from a cover 18, as shown in Figure 1 or it may be attached to a wall 24 ofqthe furnace as shown in Figure 2 or any other suitable form of support may be provided for the condensing finger to accommodate it to a location in the vapor filled space closely adjacent to the melt surface.

In the embodiment shown in Figure 3, the walls of the furnace and particularly the portion 26 of these walls above the level where the furnace contents may splash on them serves as the condensing surface. For this purpose this portion of the walls is provided with heat transfer means 28 for maintaining the inner surface of this portion of the walls at a temperature between 530 C. and 550 C., temperatures at which zinc vapor evolved from the melt will condense rapidly to liquid zinc and above the temperature at which the vapor is condensedto a solid zinc powden' Extending through the wall and about the periphery of the vessel is an annular trough 30 in which the droplets of zinc collect after they have run down portion 26 of the walls 24. From trough 30, the molten metal is conveyed to a spout and thence to a collecting apparatus or casting machine.

It will be appreciated that all inner surfaces in the furnace proper which come into contact with the vapors evolved from the melt (other than the surface of finger 16) must, of necessity, be maintained at temperatures sufiiciently above 550 C. that no condensation can occur on any surface other than the finger provided for the purpose and maintained at temperatures withinthe range of 530 C. and 550 C. Thus the arrangement described and claimed in U.S. Patent 2,781,1891is essentially distinct from the present method insofar as the patentee does not condense the metal vapor on a member positioned .Within the free vapor space in the vaporizing chamber.

In operation, the furnaces described above will be provided with means to introduce impure'raw material into i a the furnace either continuously or intermittently and with means to withdraw the product continuously or intermittently and to withdraw a portion of the impurities as they collect in order to prevent their accumulation in the bath. Such means having been known in the metallurgy of zinc, their further illustration is deemed unnecessary to .an understanding of my invention. While the product collected will usually be of sufficient purity for most purposes, it is possible to produce an even purer Zinc by returning the condensed vapors to a melting furnace of the type shown and described above, for a second vaporization and condensation. In this manner it becomespossible to obtain a zinc product which is at least 99.99% zinc metal, and is often even purer.

The drawings illustrate only some of the possible positioningsof the condensing surfaces. When a single finger is employed, as in Figure 1, 'I prefer that it be located more or less centrally in the furnace. I can, of course, employ a plurality of fingers located in one sector of the furnace or disposed in the form of'a circle or any other suitable arrangement compatible with the means for admitting the charge and any treating agents into the furnace. V

I claim:

1. A method of producing pure zinc metal from zinccontaining materials of the group consisting of impure metallic residues and reducible zinc compounds which comprises: forming a molten body of such zinc-containing material in a furnace, maintaining a temperature in the furnace at which zinc vapor is f-ormedjn a free space above the body of molten material, maintaining at least one condensing surface in said free space at a temperature between 530 C. and 550 C.; condensing metallic zinc as a liquid on said surface, and recovering the liquid zinc condensate.

2. The method of claim 1 in which the starting material is a zinc dross.

3. The method of claim 1 in which the liquid zinc product is further purified by revapor'ization and recondensation in the same manner.

References Cited in the file ofthis patent UNITED STATES PATENTS" C am'escasse Sept. 10, 1957 OTHER REFERENCES Rate of Evaporation of Zinc at Low Pressures, Clair 

1. A METHOD OF PRODUCING PURE ZINC METAL FROM ZINCCONTAINING MATERIALS OF THE GROUP CONSISTNG OF IMPURE METALLIC RESIDUES AND REDICIBLE ZINC COMPOUNDS WHICH COMPRISES: FORMING A MOLTEN BODY OF SUCH ZINC-CONTAINING MATERIAL IN A FURNACE, MAINTAINING A TEMPERATURE IN THE FURNACE AT WHICH ZINE VAPOR IS FORMED IN A FREE SPACE ABOVE THE BODY OF MOLTEN MATERIAL, MAINTAINING AT LEAST ONE CONDENSING SURFACE IN SAID FREE SPACE AT A TEMPERATURE BETWEEN 530* C. AND 550* C., CONDENSING METALLIC ZINC AS A LIQUID ON SAID SURFACE, AND RECOVERING THE LIQUID ZINC CONDENSATE. 